In such motors, commutation (ON/OFF switching) of the current(s) flowing through the winding phase(s) is accomplished electronically. The angular position of the rotor is sensed for this purpose with the aid of sensors, for example magnetically using Hall generators. From the data ascertained by the sensors and, if applicable, from other data (rotation speed, etc.), a commutation logic unit determines the points in time at which the winding phases must be energized.
It is known in this connection, in an output stage of the motor electronics, for each of the winding phases to be preceded by a bridge circuit (half or full bridge) in which semiconductor switching elements, controlled by the commutation logic unit, ensure that (as a rule) direct current of the correct polarity flows through the winding phase in question at the times determined by the commutation logic unit. This current is furnished by a so-called DC link circuit at which a so-called DC link voltage” is available. This voltage is usually generated by way of a rectifier from a delivered AC voltage, so that a pulsating DC voltage is obtained at the DC link circuit and is smoothed there using a capacitor. The capacitance of this capacitor determines the magnitude of the DC voltage component and the magnitude of the AC component of the DC link voltage and, as a result thereof, of the winding current.
The manner in which the bridge circuit is driven by the commutation logic unit is particularly problematic in such electric motors, since the low voltage values of the logic signals generated by the commutation logic unit cannot readily be used to switch those semiconductor switching elements with which a winding is connected to, or disconnected from, the pulsating DC voltage at the link circuit.
Since the electronics necessary for activating the winding phases, including the rectifier, commutation logic unit, and output stage, are often intended to be arranged inside the housing of the electric motor (this also being referred to as a “fully integrated electronic motor”), very little installation space, for the electronics, is available, especially in the case of physically small motors. The electronics moreover account for a considerable fraction of the production cost of the electronic motor.